It has been known for some time that the output of a laser could be focused to a small area of high intensity to create holes in certain types of substrates. The substrates were ones which absorbed the high energy of the laser beam to produce a resultant localized boiling and evaporation of the substrate within the path of the beam. Materials which have been found to be absorptive to laser energy have typically been metals (see U.S. Pat. No. 3,696,504), jewel minerals (see U.S. Pat. Nos. 3,601,576 and 3,527,198), and plastics (see U.S. Pat. No. 3,971,910, particularly column 2, line 38). All of these materials are opaque in varying degrees to energy beams such as lasers and are not transparent for such use. Accordingly, laser energy is absorbed which makes possible the generation of heat within the material to vaporize the material in the path of the beam, creating an opening or hole.
However, with materials which are seemingly transparent to laser energy and permit the transmission of beam energy therethrough, such as a sheet of clear glass, it has been thought that the glass would be unable to absorb and convert the laser energy to heat to form a required hole. This attitude of the prior art is demonstrated in U.S. Pat. No. 3,410,979, wherein supplementary means, in the form of a metal plate, was required behind the sheet of glass through which a drilled hole is desired. The laser beam was focused upon the interface between the glass and metal plate; heat generated by the beam impinging on the metal plate caused a localized boiling of the metal of the plate and such boiled metal was discharged back through the glass plate toward the laser to form the desired hole (see column 2, lines 10-14).
It has been discovered as part of the present invention that a certain type of laser energy, of a required wave length, is not transparent to clear glass. In addition, it has been discovered that certain processing parameters, if followed, will facilitate the generation of ultrafine channels through glass by use of the required laser energy. The dimension and quality of the channel can be controlled to a high degree of reliability, without flaws in the glass structure, and satisfactory for use as part of an electrical channel in a sensitive capitance sensor.